The last step before we do our first test render is to place and set-up the environment for reflections. For this we will go to “Rendering-Environment” click on “Environment map” and choose „bitmap“, select any hdri map you want and click ok. Open the „material editor“ by pressing „m“ key on your keyboard and drag the map from the environment tab to the material editor. Select „instance“ and change the “Mapping” to „Spherical environment“.
Before we will try our test render I will change few things. Add a new light into the scene and set the parameters for the third light together with the position as I have on the image below. Change also the “curved” part of our plane by moving it away from our model. Move the slider on the „time-frame“ to 85 and go to “Rendering-Render Setup” . Keep everything on default and click render. Go to “Rendering-Exposure Control” and click render preview. Change the exposure value to „1,5“ and click ok. At this point you can tweak your render to achieve the best result changing the materials, lights and exposure. After we are done with the testing we can set-up the render settings to higher parameters. Go to “Rendering-Render Setup” and click on the tab “Renderer”. Change the values next to “Samples” to 4 and 16. Go to the tab “Global Illumination” and change “Initial FG Point density” to 0,8 and “Rays per FG Point” to 300. Do the render again. You will notice the difference between the reflections on the „box“ model and the „sphere“ model. But why?
Reflections in theory
High reflective materials like metal have highly specular surfaces, and hence a lot of their color comes from a specular reflection of their environment. On a curved surface, any given area is able to reflect more of the environment since the surface points are capturing in several different directions more of the environment. On a flat surface, the surface is pointing in a single direction, and so capturing less of the environment in its reflection. It's actually reflecting just like the sphere, but reflecting so little of the environment that it appears to be one solid flat color. In real life the metal surface isn’t probably flat, but it’s slightly wrapped due the manufacturing, heat or water damage.
Images are courtesy of: Neil Blevins, http://www.neilblevins.com/cg_education/flat_metallic_surfaces/flat_metallic_surfaces.htm
To able to simulate real life condition we need to “damage” our material a little with a bump map. Subsequently the bump map will damage our surface on our box and help us to achieve better and more interesting reflections on a flat surface. Clone our materials and rename them. These new materials we will apply only on our box model because the sphere model is fine we don’t need to change the material there. Scroll down to “Special Purpose Maps” and click on the bump map. Choose “noise” and change the size “70”, keep everything else on default. Change the bump value to “0,5” and apply our new material to our box model. Render it again and compare. You will see that the reflections changed. At this moment you can experiment and try to achieve settings you like at most.
